Hot-blast stoves



Nov. l1, 1969 Ryo ANDQ ET AL 3,477,701

l HOT-BLAST STOVES Filed April l5, 1967 INVENTDRS RYO ANDO TERUO SHIMOTSUMA BY KANICHIRO CHIHARA ATTORNEYS 7 United States Patent O HOT-BLAST STOVES Ryo Ando, Terno Shimotsuma, and Kanichiro Chihara, l Kawasakishi, Japan, assignors to Nippon Kokan Kabushiki Kaisha, Tokyo, Japan Filed Apr. 13, 1967, Ser. No. 630,683 Claims priority, application Japan, May 16, 1966,

41/23,802; Mar. 28, 1967, 42/ 19,012

Int. Cl. F231 /00; F23m 9/00 U.S. CI. 263--19 5 Claims ABSTRACT OF THE DISCLOSURE A hot-blast stove including a gas c-ombustion chamber and a heat accumulating chamber interconnected by a dome at the top. A flow-resistance means is situated in the dome to provide uniform ow of combustion gases or hot air. Further a concave air baille is provided at the bottom of the heat accumulating chamber to prevent biased flow of `cold air therein. The flow-resistance means may take a number of forms such as a pile of spherical. members.

Background of the invention This invention relates to hot-blast stoves.

In order to improve the overall operating efliciency of a blast furnace, it is highly desirable to associate hot-blast stoves therewith to burn the gas exhausted from the top of the blast furnace and to store heat in the stove to heat the air supplied to the blast furnace -by heat exchange action and t-o recover waste heat. Although a num-ber of improvement have been made in the construction and operation of hot-blast stoves, at present the Cowper type is most widely used in modern high capacity blast furnaces. This is because the Cowper type stove is characterized by its simple construction and convenience in increasing its capacity.

In the past many improvements have been made with respect to the configuration of bricks, automation of the switching between on-gas and on-wind operations of the stove, and the materials of the bricks. However, with recent progress in pretreatments 'of raw materials to be charged into the blast furnaces, higher temperatures of the hot air are required. At the same time decrease in the coke ratio requires a substantial decrease in the quantity of heat generation in the blast furnace gas, as compared to conventional practice. Therefore, it becomes important to further increase the eciency of the blast furnace.

As an approach to these problems, it has `been the practice to add coke furnace gas for the purpose of increasing the quantity of blast generated Iby fuel gas, to utilize high load burners, program control of combustion and to switch between on-gas and on-wind at the most suitable time. However, no notable improvement has been made with respect to the non-uniform gas flow in the heat accumulating region. This non-uniform flow is believed to be the most serious disadvantage of the Cowper stove. More particularly, during on-gas operation, due to abrupt change in the direction of gas flow occurring in the dome portion of the heat accumulating chamber when the combustion gas flows from the combustion chamber into the heat accumulating chamber, the ilow of gas therein is not uniform. Further, during the on-wind operation also, due to abrupt change of air ilow 'occurring when air flows into the heat accumulating chamber from `the cold air main pipe, the flow of air becomes non-uniform. These non-uniform flows result in non-uniform temprature distribution in the heat accumulating chamber, thus substantially decreasing its efficiency of heat exchange.

More particularly, in the so-called Cowper type hotblast stove a vertical furnace is divided into a combustion Mice chamber and a checkerwork heat accumulating chamber which communicate with each other at the top or dome of the stove. During on-gas operation hot blast-furnace gas ows upwardly through the combustion chamber, reverses its direction of flow in the dome, and then flows downwardly in the heat accumulating chamber containing the checker bricks. During on-wind operation, cold air introduced into the bottom of the heat accumulating chamber blows upwardly therethrough, reverses its direction of ow in the dome, and then. flows downwardly through the combustion chamber. Such reversal of the direction of ow of the gas causes the gas to ow along one side of the combustion chamber or heat accumulating chamber and hence results in non-uniform temperature distribution as well as in a decrease in the eciency of heat exchange.

Summary of the invention One of the objects of the invention is to provide in a hot-blast stove associated with a blast furnace a uniform ow of combustion gas and air owin-g into the heat accumulating chamber, to improve the heat exchange eiciency thereof by increasing the eiective heat receiving area.

It is a further object of the invention to provide a hotblast stove in which combustion gas and air ow uniformly through the combustion and heat accumulating chambers.

Another object of this invention is to provide for blast furnaces hot-blast stoves wherein the efficiency of heat exchange in the heat accumulating chamber is increased by increasing the effective heat receiving area.

Conventional hot-blast stoves for use with blast furnaces comprise a combustion chamber, a heat accumulating chamber, a partition wall between the chambers, a dome at the top to interconnect the combustion and heat accumulating chambers, means to supply combustion gas to the combustion chamber, means to exhaust hot air from the combustion chamber, and a bottom plenum chamber at the `bottom of the heat accumulating chamber to admit cold air into and to exhaust combustion gas from the heat accumulating chamber, the heat accumulating chamber acting to store heat from combustion of the blast-furnace gas during on-gas operation and to heat cold air by giving up its stored heat thereto during onwind operation, so as to supply hot air to the blast furnace through the combustion chamber.

According to one feature of this invention a flowresistance means is non-uniformly distributed in the dome to increase the uniformity in the distribution of the flow of gas for preventing one-sided flow thereof. The resistance means may take a number of forms such as a pile of spherical members of a refractory material.

Another feature of this invention resides in the provision of a concave air baffle in the bottom plenum chamber of the heat accumulating chamber to assure uniform ow of cold air therethrough.

Yet another feature is to provide at least one perforation through the wall of the dome on the side opposite to the heat accumulating chamber to form a layer of cold air for enhancing deflection of the gas flow in the dome.

These features cooperate to assure uniform distribution of gas flow in the heat accumulating chamber, thus improving its thermal eciency.

Brief description of the drawings While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter of the invention, it is believed that the invention will be better understood from the following description taken in connection with the accompanying drawings, in which:

lFIG. 1 is a longitudinal cross-sectional view of an embodiment of a hot-blast stove constructed in accordance with the invention; and

FIG. 2 is a cross-sectional view of two forms of brick supporting posts.

Description of preferred embodiments Throughout the drawings like or corresponding parts are designated by the same reference characters.

In order to obtain a better understanding of the invention, the general construction and operation of the conventional Cowper type hot-blast stove will be considered.

Usually each installation includes three hot-blast stoves, one of which is on-wind, supplying hot air to the blast furnace, while the other two are on-gas for combustion and heat accumulation. During operation, the temperature of the hot air supplied from a particular stove is controlled by controlling the quantity of cold air supplied thereto, but when the temperature of hot air decreases to a predetermined value, the supply of hot air is interrupted and the operation of the furnace is switched to on-gas while at the same time one of the remaining stoves is switched to on-wind. The remaining stove continues its on-gas operation and will be switched to on-wind at the next switching. In this manner the switching cycle is repeated for the three hot-blast stoves.

Referringnow to FIG. 1, during the on-gas Operation a valve 1 at the bottom of the combustion chamber 2 is opened to admit a mixture of fuel gas and combustion air into the combustion chamber 2 to cause the mixture to burn therein. The combustion gas passes to a heat accumulating chamber 4 through the top of the stove where a dome 3 is situated, whereby the heat of the combustion gas is given to and accumulated by heat accumulating checkerbricks (not shown) in the chamber 4. After heat exchange, the combustion gas is exhausted by way of open valve -6 to a flue 7 through bottom plenum chamber in which are installed a plurality of posts 12a, 12b (FIG. 2) for supporting bricks in the heat accumulating charnber, it being understood that both cold air valve 8 and hot blast valve 9 are in their closed positions at this time. To switch the operation of the stove to on-wind, the Valve 1 is closed to stop the flow of fuel gas and combustion air, and the cold air valve 8 is opened to admit cold air to the bottom of heat accumulating chamber 4 through the bottom plenum chamber S. The air is heated by the heat stored in the checkerwork and the hot blast is delivered to a hot-blast valve 9 which has been opened.

-In a conventional hotblast stove of the construction described above it is clear that the ilow of combustion gas and cold air will be biased to one side. Thus, the hot combustion gas tends to flow along the right hand wall of the accumulating chamber while the cold air tends to flow along the left hand walls of the heat accumulating chamber and ycombustion chamber, as viewed in FIG. 1. It is clear that such biased or one-sided flow of gas results in nonuniform distribution of accumulated heat which in turn results in nonefticient utilization of the volume of the heat accumulating chamber, thus decreasing the etliciency of heat exchange.

In accordance with the invention, a pile of spherical members 10 of a refractory material having large heat capacity is contained in the upper portion of the heat accumulating chamber 4 to enhance the change of Vthe direction of ow of gas inside the dome 3 and to increase the uniformity in the distribution of the gas ilow. Thus, the members 10 form a pile of ow resistance bodies forming haphazard passages in the pile. The pile is positioned on top of the heat accumulating chamber and within the dome. The dome has a downwardly concave inner surface. The pile gradually increases in depth from the partition Wall away from the combustion chamber up to the inner surface of the dome, as is apparent from the upper portion of FIG. 1. In addition, at least one perforation l1 is provided through the Wall of the dome to form a layer of gas such as cold air. This arrangement prevents biased or one-sided flow of combustion gas ilowing from the combustion chamber 2 into the heat accumulating chamber, and in addition the flow of gas is nonuniformly resisted to produce uniform ow. Further, a concave air baille 12 is provided in the bottom plenum chamber 5 in which are installed posts 12a, 12b (FIG. 2) for supporting `bricks in the heat accumulating chamber, to further prevent biased flow of cold air flow into the heat accumulating chamber.

As is shown in FIG. 2, a plurality of spaced posts 12a of triangular cross-section and posts 12b of circular cross-section are provided in the bottom plenum chamber 5 to resist the ow of combustion gas and cold air flowin-g into and out of the heat accumulating chamber.

As is obvious from the foregoing description, the present invention provides a hot-blast stove for blast furnaces wherein the flow of combustion gas and cold air is changed near the dome at the top of the stove and in the bottom plenum chamber at the bottom of the heat accumulating chamber, in which posts for supporting bricks are provided, to greatly improve the thermal eciency of the heat accumulating chamber which is one of the essential elements of the hot-blast stove. Consequently, it is possible to increase the temperature of the hot-blast, save fuel consumption and prevent burning of bricks at the dome as well as leakage of gas between the combustion and heat accumulating chambers. Moreover, the distribution achieved with the hot-blast stove of the present invention is simple and cheap. Existing hot-blast stoves can be readily modified in accordance with the invention to improve their efficiency.

While the invention has been disclosed in connection with particular embodiments thereof, it will be apparent that improvements and modifications may be made without departing from the scope of the invention.

What is claimed is:

1. In a hot-blast stove, a combustion chamber, a heat accumulating chamber, a partition wall between said chambers, a dome at the top of and interconnecting said combustion chamber and said heat accumulating chamber, and a plurality of flow-resistance bodies non-uniformly distributed in said dome and delining between themselves spaces for increasing the uniformity in the distribution of the flow of gas to prevent one-sided ow thereof, said flow-resistance bodies comprising a pile of members of a refractory material forming haphazard passages therein, saidpile being positioned on top of said heat accumulating chamber and within said dome, said dome having a downwardly conc-ave inner surface and said pile gradually increasing in depth from said partition wall away from said combustion chamber up to the inner surface of said dome.

2. In a stove according to claim 1 and wherein said members are spherical. 3. In a stove according to claim 1, wherein said dome 1s f ormed with at least one perforation on the side opposite to said heat accumulating chamber to form a layer of cold air to enhance dellection of the gas flow in said dome.

4. In a stove according to claim 1, a bottom plenum chamber beneath said heat accumulating chamber and an air baille in said bottom plenum chamber extending across the latter and having an upwardly directed concave surface situated from said heat accumulating chamber by a distance which gradually increases from one side to an opposite side of said plenum chamber for preventingI biased flow of cold air into said heat accumulating chamber.

5. In a stove according to claim 1, a bottom plenum chamber beneath said heat accumulating chamber and a plurality of spaced posts installed in said bottom plenum chamber to support heat accumulating bricks in said heat accumulating chamber, some of .said pQSt having a Cir:

cular cross-section and some of said posts having a triangular cross-section.

References Cited UNITED STATES PATENTS Re. 8,814 7/1879 Cochrane et al. 263-19 1,461,357 7/1923 Kling 263-19 1,799,856 4/ 1931 McGee 263-51 2,768,822 10/1956 Frey 263-19 3,033,544 5/1962 Heuer 263-19 3,241,823 3/1966 Pentek 263-19 5 I OHN J. CAMBY, Primary Examiner U.S. Cl. X.R. 263-51 

